In recent years there has been developed a giant magnetoresistance (GMR) effect device that is made of a ferromagnetic layer, a nonmagnetic metal layer and a ferromagnetic layer laid adjacent one to another. The GMR is due to spin dependent scattering at an interface and is based on the fact that two ferromagnetic layers, when their magnetizations are switched to orient parallel or antiparallel to each other on controlled application of external magnetic filed, have a change in electrical resistance.
GMR devices have already been put to practical use as in magnetic sensors and reproducing heads in hard disk drives. Then, current is passed in a film plane, when the GMR device is called “CIP-GMR” device where CIP stands for Current In Plane. The CIP-GMR device generally makes use of an element called what is of spin valve in which an antiferromagnet is brought adjacent to one of the ferromagnets to fix spins in the one ferromagnet. On the other hand, there has also been known a GMR device called what is of “CPP” (which stands for Current Perpendicular to the Plane) type in which current is passed in a direction perpendicular to a film plane.
It is further known that generally CPP-GMR is greater in magnitude than CIP-GMR. Using such CPP-GMR, there is the proposed development to a CPP-type giant magnetoresistive effect device in which spiral magnetic domains generated by a sense current in a free magnetic layer are controlled to develop and then to a reproducing head using the device. See, the Japanese laid open patent application, for example, JP 2002-359415 A.
There are also proposals to apply a spin valve structure to a densified recording head to improve its head characteristics. See the Japanese laid open patent application, for example, JP 2002-124721 A.
There is also a proposal by the present inventors for a three-layer structure having antiparallel magnetizations identical in magnitude. See the Japanese laid open patent application, JP H09-251621 A.
A CPP-GMR device so far proposed is small in resistance, however, since its current path is small. Being poor in utility unless it is made enough smaller, the device has not yet been put to practical use.
Although in the CPP-GMR device, too, the spin valve type has been considered having an antiferromagnetic layer 81 brought adjacent to a ferromagnetic fixed layer 82 as shown in FIG. 10, the antiferromagnetic layer 81 is larger in resistance than a GMR film made of a ferromagnetic free layer 84, a nonmagnetic conductive layer 83 and the ferromagnetic fixed layer 82 to an extent that the spin valve element then will generally have to have its rate of resistance change as small as less than 1% and its resistance change ΔR that is small, too. This becomes a primary and large factor that prevents a CPP-GMR device from its practical use.
Therefore, a problem that prevents a conventional spin valve type CPP-GMR device from its practical use is that it is small in resistance change ΔR and rate of change of magnetic resistance.
The present inventors have discovered that coupling a pair of ferromagnetic layers antiparallel to each other via a nonmagnetic metal layer while using this three-layer structure (SyAF) with different magnitudes of magnetization for a free and/or a fixed layer gives rise to a CPP-GMR device of spin valve type of which ΔR is large and the rate of change of magnetic resistance is increased to 8% or more and then have reached the present invention.